1. Field of the Invention
The present invention relates generally to electronic devices employing therein an electronic element with opposite electrodes on its principal planes, and more particularly, to electronic modules with an elastic support mechanism for an electronic element mounted therein having spring contact pieces in contact with respective electrodes of the electronic element for elastic support of the element as interposed therebetween.
2. Description of the Prior Art
Conventionally, many electronic devices include positive thermistor devices for use in current limiter circuitry. Thus, thermistor devices have been widely used in the manufacture of several types of electric circuitry or modules, including motor activation controller circuitry for electric refrigerators, electronic demagnetization circuitry for television receivers, monitor display tube units, and other applications.
One typical configuration of a prior art positive thermistor device is shown in FIGS. 13 and 14, wherein this device is generally designated by the numeral 1. This conventional positive thermistor device 1 essentially consists of a casing body or base 3, a positive thermistor element 4 held therein, a pair of first and second terminal members 5, 6, and a lid or cover 2 attached to the base 3 to close the upper opening thereof.
As shown, the positive thermistor element 4 exhibits a disk-like shape having opposite surfaces on which first and second electrodes 7, 8 are disposed respectively. This positive thermistor element 4 is centrally inserted into the inside space of the base 3, with the electrodes 7, 8 facing the right and left sides thereof, as shown in FIG. 14.
The first and second terminal members 5, 6 are assembled within the inside space of casing base 3 in such a way that these members 5, 6 support both sides of the opposed electrodes 7, 8 of the positive thermistor element 4. Each terminal member 5, 6 may be an elastic conductive plate of a chosen metallic material. The first terminal member 5 includes a pair of spring contact pieces 9, 10 having a W-shaped profile as a whole, and also a hollow tube socket 11 with a longitudinal gap for receiving therein a known connector pin (not shown) associated therewith to provide electrical connection therebetween. A wave shaped plate constituting the W-shaped spring contact pieces 9, 10 and the socket 11 may be integrally formed in the terminal member 5 by known welding or caulking techniques. The second terminal member 6 is similar in structure to the first terminal 5; it has W-shaped spring contact pieces 12, 13 and connector-pin socket 14.
After assembly within the casing base 3, the spring contact pieces 9, 10 of the first terminal member 5 serve to apply compressive force onto the first electrode 7 due to its inherent elastic nature. Similarly, the spring contact pieces 12, 13 of the second terminal member 6 apply compressive force to the second electrode 8. This may enable the positive thermistor element 4 to be elastically supported or suspended between the terminal members 5, 6 while the element 4 is interposed between one pair of spring contact pieces 9, 10 and the other pair of contact pieces 12, 13.
Additionally, a mica plate 15 may be disposed around the outer periphery of the positive thermistor element 4. This mica plate 15 exhibits a circular shape. When engaged with the outer periphery of thermistor element 4, this plate 15 acts to facilitate appropriate positioning (hereinafter referred to as "position-determination") of thermistor 4 inside base 3.
After the positive thermistor element 4 and terminal members 5, 6 are assembled within the casing base 3, the cover 2 is attached thereto so that it closes the upper opening of the casing body 3. This cover 2 is a rectangular plate member having at its two corresponding corners two holes 16, 17 to permit insertion of external connector pins into the sockets 11, 14 through these holes respectively.
Another prior known positive thermistor device 1a is shown in FIGS. 16 to 18. As is readily seen by comparison of the illustration of FIG. 16 to that of FIG. 14, this prior art device is similar in structure to the previous device; accordingly, like reference characters are used to designate like parts or components with a redundant explanation thereof being omitted herein.
As can be seen from FIG. 16, the positive thermistor device 1a is structurally different from that of FIG. 14 to the extent that a first terminal member 5a has a W-shaped pair of spring contact pieces 9a, 10a extending vertically, rather than horizontally as in the previous prior art device 1, best shown in FIG. 14, thereby preventing these contact pieces 9a, 10a from directly opposing their associated spring contact pieces 12, 13 of the other, second terminal member 6. Such vertical facing relation of spring contact pieces 9a, 10a versus the opposite spring contact pieces 12, 13 may also be seen in FIGS. 17 and 18. FIGS. 17 and 18 show a plan view and side view, respectively, of the device shown in FIG. 16.
With the prior art positive thermistor devices 1, 1a, after a long time has elapsed after installation thereof, the structure of the positive thermistor element 4 may become physically degraded. If this is the case, abnormal heat generation may take place therein causing sparks to occur during operation, which results in the positive thermistor element 4 being destroyed due to occurrence of such sparks. When the thermistor element 4 is destroyed, it breaks into several fragments that can disperse within the closed inside space as defined by the casing base 3 and cover 2 attached thereto.
Such a "malfunction mode" phenomenon can lead to a more serious malfunction mode, which will be discussed in more detail below with reference to FIGS. 15A and 15B for the positive thermistor device of FIGS. 13 and 14, and with reference to FIGS. 19 to 21 for the device 1a shown in FIGS. 16 to 18, respectively.
In the positive thermistor device 1 of FIGS. 13 and 14, when sparks occur, the resulting positive thermistor element 4 experiences occurrence of several cracks 18 therein, as shown in FIG. 15A. Even under such a condition, specific cracked portions 19, each of which is elastically supported by the opposed spring contact pieces 9, 10 (or 12, 13) at its opposite sides, continue to stably be held thereat as shown in FIG. 15B, while the remaining fragments disperse. Accordingly, a power supply may continuously be fed by way of such residual components 19 of the thermistor element 4, causing these residual components 19 and their associative spring contact pieces 9, 10, 12, 13 to melt, in turn producing an alloy that exhibits some conductivity. As a result, an electrical short can be formed between the terminal members 5, 6. This adversely serves to accelerate further generation of abnormal heat. This will possibly force the device to go into a further malfunction mode which can, in turn, lead to unwanted softening of the casing base 3.
Furthermore, in the positive thermistor device 1, since the mica plate 15 is arranged therein, certain peripheral portions 20 of the positive thermistor element 4 which are directly in contact with the mica plate 15 tend to also be prevented from flying away as fragments, in most cases. Such peripheral portions 20 also contribute to the formation of alloy together with the aforementioned portions 19 being elastically supported by spring contact pieces 9, 10, 12, 13, with the result of increasing the amount of materials for producing the alloy. This may exacerbate the malfunction of the device, which may cause the softening of base 3 to become more serious.
On the other hand, in the positive thermistor device 1a shown in FIGS. 16 to 18, the positive thermistor element 4 experiences occurrence of cracks 21 due to generation of sparks, as shown in FIG. 20A. In this case, the thermistor element 4 is broken into several fragments that tend to disperse. At this time, since the spring contact pieces 9a, 10a and their opposed contact pieces 12, 13 are not identical to each other in a spring-force application direction, any dispersed fragments will be positionally offset from their original positions. However, since the distance 22 between a respective one of the spring contact pieces 9a, 10a and a corresponding one of opposed spring contact pieces 12, 13 associated therewith is designed so that the distance is less than the thickness 23 of the positive thermistor element 4 in a free state where the element 4 is removed as shown in FIG. 19, one part 24 thereof will possibly be held at its original position as a result of the fact that it happens to be gripped or hung between the spring contact piece 9a and/or 10a on one hand and elements 12 and/or 13 on the other hand, as shown in FIGS. 20A and 20B. If this is the case, application of a power supply may continue via such a hung portion 24 causing, in a similar way as in the previous device 1, this portion 24 and any one of contact pieces 9a, 10a, 12, 13 to melt, in turn producing an alloy, whereby the terminal members 5a, 6 are electrically shorted therebetween so that abnormal heat generation is accelerated. This, in turn, may lead to a further serious malfunction mode where the casing base 3 is softened undesirably. Regarding the presence of the mica plate 15, the previous discussions may also be true for this device 1a. Namely, in the positive thermistor device 1a, since the mica plate 15 is arranged therein, certain peripheral portions 25 of the positive thermistor element 4 which are directly in contact with the mica plate 15 are prevented from flying away as fragments in most cases, as shown in FIG. 20B, in a similar manner as in the above positive thermistor device 1. Such peripheral portions 25 also give rise to generation of an alloy, which adds to the amount of material for producing the alloy. This may serve to worsen the malfunction mode of the device, causing a softening of base 3 to become more serious.
The aforesaid problems will not exclusively arise with positive thermistor devices, and will possibly take place in other types of electronic components or devices, insofar as these other types of components employ therein an electronic element that is electrically fed and elastically supported by using similar contact members associated therewith, which element is susceptible to degradation and eventual destruction due to long use.